The present invention is related to an adjustable-crown roll, comprising a stationary roll axle which is supported on the machine frame or equivalent by means of articulated bearings, a roll mantle arranged to revolve on the axle, and hydrostatic loading members or an equivalent pressure fluid chamber or series of chambers arranged in a space between the roll axle and the roll mantle. By means of the loading members or equivalent, the profile of the nip, which can be formed with a counter-roll of the roll, can be regulated. The loading members or equivalent are fitted substantially in the plane of at least the nip. A support bushing arranged concentrically with the roll mantle is attached to at least one end of the roll mantle to revolve along with the roll mantle.
At present, the construction of adjustable-crown rolls is usually such that the roll mantle is arranged to revolve on the stationary roll axle, on which the roll mantle is supported in a suitable way, e.g. by means of hydraulic loading members, so that by means of the loading members, the deflection of the roll mantle and the roll axle in relation to one another can be adjusted in a desired way.
Generally, the roll mantle is additionally supported on the roll axle by means of bearings placed at the ends of the mantle, in particular by means of roller bearings or equivalent rolling-contact bearings which also receive the axial forces. Such a construction involves a number of drawbacks, especially when it is applied to hot rolls and to rolls provided with a drive gear. One of these drawbacks is that the end bearing of a roll requires very precise machinings to be made into the roll mantle and, moreover, a rolling-contact bearing at the end of the mantle makes the drive of the roll more difficult.
If the rolling-contact bearing is replaced by some other solution, the above problems can be avoided. Problems of the rolls with no rolling-contact bearings are, however, the grinding of the roll and in particular the requirements of precision imposed on the grinding as well as the receiving of the axial forces.
Further, it is a problem of hot rolls that a certain viscosity is required from the oil circulating in the rolls in order that the lubrication of the bearings should operate properly. In hot rolls, the oil may become excessively hot, which may, in the worst case, result in seizing of the bearings.
In hot rolls, attempts have been made to avoid said problem, e.g. by placing the end bearings of the roll mantle outside the roll mantle. This has been the case, e.g. in the solution described in FI Patent Application No. 853223 (corresponding to U.S. Pat. No. 4,679,287, Beloit Corp.) in which particular extension bushings have been attached to the ends of the roll mantle, by whose means the roll mantle has been mounted on the roll axle from outside the mantle. Therein, rolling-contact bearings are used, which are placed between said extension bushing and the roll axle. The arrangement described in this publication, however, requires quite complicated sealing and insulation arrangements at the ends of the roll so that the roll can be used as a hot roll so that excessive heat cannot affect the end bearings. Thus, in view of the drive of the roll, the solution of this publication is not fully free from problems, and fitting of the drive gear at the roll end cannot be accomplished in an easy and simple way.
On the other hand, FI Published Patent Application No. 79,895 (corresponding to U.S. Pat. No. 4,520,723, Kleinewefers GmbH), describes an arrangement in which conventional rolling-contact bearings at the roll ends are replaced by hydrostatic bearings. In view of the drive of the roll, this can be probably considered an improvement, but the solution of this publication cannot be applied to a hot roll as such. This already comes from the drawbacks discussed above, in particular from the fact that the heat can affect the bearing at the roll end directly, whereby extremely high requirements are imposed on the viscosity of the oil so that the hydrostatic bearing may operate in a desired way.
In practice, hot rolls in a paper machine must always be provided with a drive in order that the roll becomes warm evenly in the direction of the circumference. For example, the counter-roll drive applied in supercalenders cannot be used in hot rolls because of the high surface temperature. The surface temperatures may be of an order of 200.degree. C.
Thus, the object of the present invention is to provide an adjustable-crown roll, in particular, a hot roll, by whose means the drawbacks related to the present day technology are avoided.
A further object of the invention is to provide a roll whose roll mantle is as simple as possible without undue and precise machinings.